From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751991AbcAWIRN (ORCPT ); Sat, 23 Jan 2016 03:17:13 -0500 Received: from mail-pa0-f67.google.com ([209.85.220.67]:35464 "EHLO mail-pa0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751581AbcAWIRL (ORCPT ); Sat, 23 Jan 2016 03:17:11 -0500 From: Sergey Senozhatsky To: Andrew Morton Cc: Petr Mladek , Jan Kara , Tejun Heo , Kyle McMartin , Dave Jones , Calvin Owens , linux-kernel@vger.kernel.org, Sergey Senozhatsky , Sergey Senozhatsky Subject: [RFC][PATCH v3 0/4] let printk()/console_trylock() callers to cond_resched() Date: Sat, 23 Jan 2016 17:15:09 +0900 Message-Id: <1453536913-9545-1-git-send-email-sergey.senozhatsky@gmail.com> X-Mailer: git-send-email 2.7.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [was: cond_resched() some of console_trylock callers] Hello, console_unlock() allows to cond_resched() if its caller has set `console_may_schedule' to 1 (this functionality present since commit 'printk: do cond_resched() between lines while outputting to consoles'). The rules are: -- console_lock() always sets `console_may_schedule' to 1 -- console_trylock() always sets `console_may_schedule' to 0 printk() calls console_unlock() with preemption desabled, which basically can lead to RCU stalls, watchdog soft lockups, etc. if something is simultaneously calling printk() frequent enough (IOW, console_sem owner always has new data to send to console divers and can't leave console_unlock() for a long time). printk()->console_trylock() callers do not necessarily execute in atomic contexts, and some of them can cond_resched() in console_unlock(). console_trylock() can set `console_may_schedule' to 1 (allow cond_resched() later in consoe_unlock()) when it's safe. 0001 addresses a theoretical loss of printk messages. 0002 is an optional optimization patch 0003 drops console_trylock_for_printk 0004 lets some of printk()/console_trylock() callers to cond_resched() in console_unlock() v2-v3 (thanks to Petr Mladek for reviews): -- do not call can_use_console() on every iteration in console_unlock() (Petr Mladek) -- move "This stops the holder of console_sem.." comment (noted by Petr Mladek) -- take extra care of !PREEMPT_COUNT kernels (Petr Mladek) -- call_console_drivers() still must check cpu_online && CON_ANYTIME (Petr Mladek) -- removed console_trylock_for_printk() (noted by Petr Mladek) v1-v2: -- make have_callable_console() available for !PRINTK configs (lkp@intel.com) -- take care of RCU preempt kernels in console_trylock() Sergey Senozhatsky (4): printk: move can_use_console out of console_trylock_for_printk printk: do not console_cont_flush() on every jump to again printk: remove console_trylock_for_printk printk: set may_schedule for some of console_trylock callers kernel/printk/printk.c | 121 ++++++++++++++++++++++--------------------------- 1 file changed, 55 insertions(+), 66 deletions(-) -- 2.7.0